Microelectronic devices, such as semiconductors or integrated circuits, can include millions of electronic circuit devices such as transistors, capacitors, etc. To further increase the density of devices found on integrated circuits, even smaller feature sizes are desired. To achieve these smaller feature sizes, the size of conductive lines, vias, and interconnects, gates, etc. must be reduced. Reliable formation of multilevel interconnect structures is also necessary to increase circuit density and quality. Advances in fabrication techniques have enabled use of copper for conductive lines, interconnects, vias, and other structures. However, electromigration in interconnect structures becomes a greater hurdle to overcome, with decreased feature size and the increased use of copper for interconnections.
Tantalum nitride (TaN) is a copper barrier at film thicknesses greater than 10 A, where the film is continuous. However, because a Ta atom is about 4 A in diameter, TaN films around 5 A thick are not continuous. For smaller nodes where thinner TaN is required, TaN by itself may be a discontinuous film, thus limiting its copper barrier properties. Current methods include a Ta layer on top of a TaN layer, which acts as a wetting layer for copper and provides the continuity of a barrier film. For smaller nodes (less than 32 nm), however, this method leads to larger line resistance and hence is not an adequate solution.
Physical vapor deposited (PVD) tantalum nitride (TaN) is a standard material for diffusion bathers in copper interconnections. Due to poor adhesion of copper to the TaN, a tantalum liner is also used to enhance the durability of the interconnect structures. As the dimension of copper interconnections are being reduced to sub-20 nm, the non-conformal nature of PVD TaN barrier plus Ta liner has caused issues, such as copper gap fill voiding and high line resistance. Atomic layer deposition (ALD) TaN is being used as an advanced technology with better conformality; however, the film quality of ALD TaN still needs significant improvements.
Therefore, there is a need in the art for thin layers that are effective copper barriers.